The invention relates to miniaturization of electronic components and, in particular, to using a micromachined magnetostatic relay in commutating a DC motor.
Manufacturers and users of electrical and electronic components strive to reduce the size and increase the reliability of these components and the systems in which they are used. Miniaturization of components leads to more compact and lightweight systems, which increases the range of uses for these systems and decreases the costs associated with transporting and using these systems. Improving component reliability lengthens the lifespan and enhances the performance of systems in which the components are used.
Miniaturization and reliability improvements are particularly important in areas such as space exploration and satellite communications. The cost of launching equipment from the Earth""s surface is directly related to the size and weight of the equipment, and even modest reductions in equipment size produce large reductions in cost. Likewise, improving the reliability of components used in spaceborne systems extends and improves the performance of these systems, thus reducing the associated costs. In general, each newly developed generation of space oriented components and systems must meet or exceed the performance and cost standards set by previous generations.
One example of commonly used components for which size and reliability are particularly important is DC electric motors. DC motors are used widely as motive devices for linear and rotary drives in spaceborne applications. As gains have been made in the miniaturization of DC motors, the size, weight, and complexity of DC motor systems have become dominated by the commutation and control electronics that drive the motors. The disparity between the size of the motor and the size of its control electronics is particularly noticeable in a highly miniaturized motor, such as a commercially available 3-mm diameter motor, the commutation and control electronics of which are more than ten times larger than the motor itself. Even modest reductions in the power budget, complexity, mass, and volume of components such as these produce tremendous gains in the cost and reliability of spaceborne systems.
In recognition of the above, the inventors have developed micromachined magnetostatic relays or switches that are highly miniaturized and highly reliable. The switches are made very small using micromachining fabrication techniques, and the materials are carefully selected to provide high reliability. The switches are useful in a wide variety of microelectronic mechanical system (MEMS) applications, particularly in the miniaturization of DC electric motors. For example, in one embodiment of the invention, the switches are used as relays in a MEMS circuit that replaces the conventional commutation and control electronics in a DC motor. This MEMS circuit is much smaller than the DC motor itself, so the size of the motor, not the size of the commutation electronics, is most critical in space constrained applications. The magnetostatic switch requires no biasing current or voltage and is useful in directly switching loads.
In one aspect, the invention features a DC motor having a plurality of windings and at least one magnetostatic relay positioned to activate in the presence of a magnetic field. Each relay is connected electrically to at least one corresponding winding and to power. The motor also includes a magnetic rotor having at least one pole positioned to induce a magnetic field in each magnetostatic relay when passing by the relay.
In some embodiments, the windings are arranged in pairs of primary and secondary windings, and each relay connects to a corresponding one of the pairs of windings. In some cases the secondary windings all connect to a common node, and each of the primary windings connects to the corresponding relay. In one implementation, the motor is a four-pole, three-phase motor that includes three relays separated from each other by approximately 120xc2x0.
In another aspect, the invention features a DC motor having a plurality of windings and at least one magnetostatic relay connected electrically to at least one of the windings and to power. Each relay has at least one substrate formed from a non-conductive or semiconductive material, a springing beam formed on the substrate, and two electrically conductive elements, one of which is formed on the springing beam. The electrically conductive-elements together define at least two-switching states, including an open state in which the conductive elements are physically separated from each other, and a closed state in which the conductive elements physically contact each other. The springing beam includes a magnetic material which, in the presence of a magnetic field, creates an actuation force that causes the electrically conductive elements to apply power to or remove power from at least one of the windings by switching from one of the switching states to another of the switching states. The motor also includes a magnetic rotor having at least one pole positioned to induce a magnetic field in each magnetostatic relay when passing by the relay.
In another aspect, the invention features a method for use in commutating a DC motor. The method includes rotating a magnetic rotor to induce a magnetic field in at least one magnetostatic relay in the motor. Each relay is activated in response to the magnetic field to deliver power to at least one winding in the motor.
In some embodiments, each relay first delivers power through a corresponding primary winding and then through a corresponding secondary winding to a common node. Other embodiments include activating each relay four times during one rotation of the magnetic rotor.
Other embodiments and advantages will become apparent from the following description and from the claims.